The invention herein described was made in the course of or under a contract or subcontract thereunder with the Department of the Army.
This invention relates to nozzles and more particularly to a nozzle array having a minimum constraint support configuration adapted for minimizing corner shear strains resulting from thermal deformation of the nozzle array and for providing an elastic restoring force to a plastically deformed nozzle array.
In the operation of high powered chemical lasers a population inversion within an optical cavity region of the laser is created by expanding hot gases through a nozzle array by means well known in the art. The passage of hot gases, typically having a gas temperature in excess of four thousand degrees Rankine (4000.degree. R.), through the nozzle significantly increases the temperature of the nozzle producing thermal distortion therein. In chemical lasers employing harsh gases such as fluorine, the nozzle must be constructed of material compatible with the harsh gas environment and the nozzle must maintain its structural integrity during repeated operation cycles. Nozzles constructed of pure nickel material are compatible for use with the harsh environment of fluorine gas. However, at the operating temperatures required of chemical lasers, the nickel nozzles undergo plastic thermal deformation resulting in unwanted distortions which are not restored during the cool-down portion of the operation cycle. The utilization of nickel material for the nozzle results in thermal strains being generated therein which seriously limit the fatigue lifetime of the nozzle structure.
The extremes in the gas temperatures combined with the reactive nature of the fluorine environment generally prohibits the use of sliding joints, seals, etc., typically utilized for compensating thermal distortion. Typically thermal expansion of a restrained nozzle array formed of nickel material results in unacceptably high plastic strains in the individual nickel nozzle elements, and results in excessive deflection of the nozzle array into the optical cavity, both of which have a deleterious effect on laser performance. Moreover, if the thermal expansion of a nozzle array formed of nickel material is unrestrained and accommodated by the use of flexible combustion chamber walls and/or a floating frame concept, an undesirable deformation pattern is generated producing unacceptably high shear strains near the corners of the array resulting in low operating life of the nozzle array. This undesirable deformation pattern is typically due to the low shear stiffness of the nozzle array relative to the stiffness of its support structures and the inability to completely match the transient thermal response of the support structure to the nozzle array.